blue/white selection problem

Frank O. Fackelmayer Frank.Fackelmayer at
Tue May 16 10:49:53 EST 2000

One possible reason could be overdigestion of the vector, resulting in
damaged ends. These could still be ligated in some cases, leading to
white colonies. As you say the vector is from a kit, it is possible that
the DNA has been damaged by multiple freeze-thaws. 

Anyway, I assume there are not only white but also blue colonies. Check
some of those to see if they might have the insert. Blue-white selection
is sometimes misleading. Especially with short inserts it is quite
common to see blue or slightly blueish colonies that HAVE the insert,
while white colonies haven´t. I´ve had clonings where the blueish
colonies had the insert, but neither the blue nor the white ones. Then I
had positive clones that where perfectly blue...

Well, as a consequence, I´m hardly doing blue-white selection after all nowadays.


> I am using blue/white selection to choose colonies with my insert.
> Unfortunately, my white colonies don't have inserts.  What could be
> causing this.
> Rodney Earl Pettway
> USDA-ARS Cereal Disease Lab
> University of Minnesota
> St. Paul, MN., 55108

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